A sitcom about a longtime gay couple who constantly squabble and snap at each other may not seem to have much currency in the 21st century. But when the lavender Bickersons are portrayed by Ian McKellen and Derek Jacobi, who needs to be up to date?

Freddie Thornhill (McKellen, "Lord of the Rings") is an actor of a certain age whose only income is whatever he still gets in royalties from a cigarette commercial made years before. Nonetheless, he still lives the part of a major thespian, asking his partner, Stuart Bixby (Jacobi, "Last Tango in Halifax"), every day if he's received a call from his agent. The answer, of course, is always the same.

Freddie and Stuart have been together for 48 years, although Stuart has yet to tell his mother of the nature of their relationship: He's waiting for the right time, he says. When might that be, Freddie hisses: When she's dead?

They have a feisty, sex-starved best friend named Violet Crosby (Frances de la Tour, "Harry Potter and the Deathly Hallows") and a couple of other elderly friends, the constantly confused Penelope (Marcia Warren) and the sharp-tongued Mason (Philip Voss).

Watching "Vicious," created by Gary Janetti ("Family Guy," "Will & Grace") and premiering Sunday on PBS, is not unlike going to a West End comedy. McKellen and Jacobi don't act the way we're used to seeing them perform in film and television, but, rather, as if they are holding forth on a real stage. Dialogue, much of it deliciously laced with arsenic, is not so much delivered as it is declaimed. Punch lines are punched hard, pauses timed to comedic perfection and facial expressions exaggerated for emphasis.

If you're familiar with some of the great Brit-coms of the past - "Keeping Up Appearances," "Are You Being Served," for example - you probably know the British fondness for repeating bits from episode to episode. American sitcoms do it as well, of course, but perhaps with less obvious purpose. With a British sitcom, one character will say something inane in one episode and repeat it thereafter, expanding the comedic "rule of three" to double digits over multiple episodes.

In the case of "Vicious," for example, every time the young, hunky and happily straight upstairs neighbor Ash (Iwan Rheon, "Game of Thrones") shows up at the door, Stuart reintroduces him to their ever-present guest Violet, as if they haven't met many times before.

Another way you know this is a British show (beyond the obvious: that it's about Britons, starring Britons, living in Britain) is that "Vicious" is almost unrelenting in its, well, viciousness. Moments of sincere affection between Freddie and Stuart are fleeting and rare. If this were an American sitcom, punches, if not punch lines, would be pulled, for fear of alienating the audience.

So leave your politically correct concerns on the doorstep, sit back, and let the venom wash over you like a sleet storm. McKellen and Jacobi, who are, of course, giants of their profession, are clearly having a lark with "Vicious," and you'd be foolish not to want in on the fun.